The present invention relates generally to bone screw screwdrivers and more particularly to a screwdriver that securely, positively locks the screw to the screwdriver.
The medical arts have advanced substantially in both design and materials. As is known in the orthopaedic field, various types of bone nails and screws are used for fixing implants and fractures where the fastener is attached to the bone. Bone screws may be implanted into the spine for stabilization in patients with spinal deformities and other injuries. Bone screws may hold rods which hold the back stiff while the vertebra are fused together. Thus, it is known to use bone screws for spinal fixation, as well as for other types of bone fixation or stabilization or to secure other implants. A high degree of precision is required to securely retain the devices in a proper working position.
Surgeons performing various orthopaedic operations work under difficult operating conditions. Not only must a surgeon focus his attention on the operating site and any complications which may arise, but the operating area is often not freely accessible. This often creates difficulty in fitting and positioning bone screws and/or other implants.
Normally during attachment of a bone screw, the surgeon requires one hand to expose tissue and hold the bone screw in position while the other hand rotatably drives the screw. In one current technique, bone screws are held by pliers in one hand of the surgeon while rotatably driven by a driver with the other hand. The non-positive lock between the pliers, screwdriver and bone screw make attachment of the screw more difficult, awkward and time consuming.
One screwdriver, as shown in U.S. Pat. No. 5,139,499, includes a radially compressible collet-like front portion that engages the axial bore of a screw. The front portion of the screwdriver deforms to create a spring bias to hold the screw to the driver. A possible problem is that the screw may not be fully engaged to the screwdriver. Furthermore, the material of the spring portion may fatigue or shear without notice during insertion of the screwdriver into the screw.
Another screwdriver, as shown in U.S. Pat. No. 4,963,144, has a longitudinal drive tube which is interfit with the threaded head of a bone screw. An associated jam rod is locked into place on the screw, to prevent its removal from the drive tube. A disadvantage of this system is the requirement for the head of the screw to include threads.
It is important that the screw does not disengage from the screwdriver when the screwdriver is driven into the bone. In areas of operation, such as the spinal column, a positive lock both axially and radially between the screw and screwdriver is important for proper placement of the bone screw. It is beneficial that the fastener used in a surgical procedure be retained by the driver so that the surgeon can positively position the fastener and rotatably drive it using one hand.